EXCLUSIVE: Castle executive producer/co-showrunner Rene Echevarria has departed the ABC dramedy series after not being able to reach a new deal with producer ABC Studios. Echevarria co-ran Castle with creator/executive producer Andrew W. Marlowe this season, which saw the quirky mystery show establish itself as ABC’s most promising new hourlong series in years. Castle’s ratings rise in the current second season earned the Nathan Fillion starrer an early renewal for next fall. Marlowe will now be the series’ sole showrunner. Echevarria, who co-created/executive produced USA’s 4400 and  executive produced Medium when it ran on NBC has several projects in the hopper, including the MTV pilot Teen Wolf, on which he serves as an executive producer.